Kevin Ryan is a fictional character portrayed by Seamus Dever on ABC crime series Castle.
Detective Kevin Ryan, formerly a narcotics division cop, now works alongside Esposito as part of Beckett's team. He and Esposito regularly tease Beckett, like when they discovered that she had embarked on a brief modeling career during her teens, but they are otherwise incredibly protective of her and ultimately treat her like one of the guys. In the season 1 episode "Little Girl Lost," Ryan is revealed to have a new girlfriend named Jenny; she is often mentioned, and routinely calls him to check up on him, but her first appearance comes in "The Mistress Always Spanks Twice", where she was portrayed by Dever's real-life wife, Juliana. Jenny returned in the Season 3 episode "Nikki Heat," where Ryan proposes to her in the middle of the homicide bullpen. In the fourth season, he is shown complaining about how stressful and complicated planning a wedding is. His love life and the fact he is in nearly-constant communication with his girlfriend/fiancee makes him subject to much teasing from his partner, so when Esposito begins dating Lanie, he relished turning the tables on his friend. Little is known about Ryan's family except that he grew up in the Bronx with an unnamed number of sisters, one of whom has a son, as Ryan makes reference to a nephew who loves the Captain Underpants book series. He also attended Catholic school for 12 years, as was mentioned during the episode "Knockdown."